The present invention generally relates to semiconductor processing, and in particular to a system and method for post baking a chemically amplified photoresist.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there have been, and continue to be, efforts toward scaling down device dimensions on semiconductor wafers. In order to accomplish higher device density, smaller and smaller features sizes are required. These may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and surface geometry of corners and edges of various features.
High resolution lithographic processes are used to achieve small features with close spacing between adjacent features. In general, lithography refers to processes for pattern transfer between various media. Lithography is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist. The film is selectively exposed with radiation (such as optical light, x-rays, or an electron beam) through an intervening master template, the mask, forming a particular pattern. Areas of the coating exposed through the mask become either more or less soluble (depending on the type of coating) in a particular solvent developer. The more soluble areas are removed in a developing process leaving the less soluble areas in the form of a patterned coating.
Shorter wavelength light, in the 193 to 248 nm range, is presently used to pattern small features. The intensity of common sources for such light, is comparatively low. To keep processing times under control, sensitive photoresists are employed. A typical highly sensitive photoresist is a chemically amplified photoresist. A chemically amplified photoresist is one in which exposure to actinic radiation produces a catalyst for a reaction that alters the solubility of the resist. A common example is a positive tone resist containing a photoacid generator that generates an acid catalyst on exposure to actinic radiation. The photo-generated acid may catalyze a deprotection reaction that increases the solubility of the photoresist in aqueous base.
In the typical case, a post exposure baking (PEB) step is required to cause the photo-generated catalyst to diffuse and react within the photoresist coating. The PEB step has a significant effect on the quality of pattern transfer. If the PEB step is too long or the resist is overheated, the catalyst can migrate outside of the exposed portion of the resist into surrounding unexposed areas. If the PEB step is too short or the resist is underheated, diffusion and reaction of the catalyst may be unduly limited resulting in an inadequate solubility contrast between exposed and unexposed regions of the photoresist. There is an unsatisfied need for systems and methods of effectively controlling PEB of chemically amplified photoresists.
The invention provides systems and methods for controlling resist baking processes, such as PEB of chemically amplified photoresists. A system of the invention provides a baking plate through which hot fluids and cold fluids may be alternately circulated. The system takes measurements relating to temperature of the baking plate, temperature of the resist, and/or extent of the baking process. Using this data, the system controls the baking temperature and/or the overall extent of the baking process through control over the flow of hot and cold fluids. By alternating between hot and cold fluid circulation, systems of the invention provide rapidly responsive temperature control and/or abrupt termination of baking. Control over the baking process is further increased by implementing flow and process control separately over each of a plurality of different portions of a baking plate.
One aspect of the invention provides a baking system including a baking plate within which are formed passages through which fluids may be circulated, a hot fluid supply, a cold fluid supply, a flow control system, a controller, and a measuring system, wherein the controller, in response to data provided by the measuring system, directs the flow control system to supply the passages with fluid from the hot fluid supply and/or fluid from the cold fluid supply, depending on whether the baking plate needs to be heated or cooled.
Another aspect of the invention provides a baking system including a baking plate within which are formed a plurality of segregated groups of passages, a portion of the baking plate being associated with each of the segregated groups of passages, a hot fluid supply, a cold fluid supply, and a flow control system that independently for a plurality of the segregated groups of passages controls the circulation of fluid from the hot fluid supply and fluid from the cold fluid supply, whereby the plurality of segregated groups of passages may be supplied with either hot or cold fluid and associated portions of the baking plate may be either heated or cooled.
A further aspect of the invention provides method of post baking a chemically amplified photoresist including placing a photoresist coated substrate on a baking plate, circulating hot fluid through the baking plate to heat the photoresist, and then circulating cold fluid through the baking plate to cool the photoresist.
A still further aspect of the invention provides a system for post baking a chemically amplified photoresist coating on a substrate including means for circulating hot and cold fluids through a baking plate and means for controlling the post baking of the chemically amplified photoresist via controlling the circulation of hot and cold fluids through the baking plate.